4-Phenyl-4-oxo-2-butenoate derivatives are useful in the fields of medicines, pesticides, perfumes, and the like and particularly are important key compounds as intermediates for medicines. Various processes for producing the derivatives have been reported and, for example, a process for esterification of 4-phenyl-4-oxo-2-butenoic acid (JP-A-62-103042 and JP-A-63-130564) has been disclosed. In this process, however, 4-phenyl-4-oxo-2-butenoic acid derivatives as starting materials are not commercially available and are difficult to obtain. In the case of synthesizing the starting material 4-phenyl-4-oxo-2-butenoic acid derivatives, Friedel-Crafts reaction of aromatic compounds using maleic anhydride and aluminum chloride (J. Am. Chem. Soc., 70, 3356 (1948)) and the like have been known but the reaction takes a long period of time. Moreover, in the work-up after completion of the reaction, since both of the aimed 4-Phenyl-4-oxo-2-butenoic acid derivative and aluminum hydroxide are contained in an aqueous layer, separation thereof requires a special operation such as steam distillation and hence it is very difficult to conduct the operation on an industrial scale. Aldol condensation of an acetophenone with glyoxylic acid (JP-B-52-39020) or the like process has also been reported but this case also requires a long period of time for the reaction and operations are complicated. Furthermore, in these processes, it is necessary to esterify the 4-phenyl-4-oxo-2-butenoic acid derivative in a next step and the yield of the aimed 4-phenyl-4-oxo-2-butenoate derivative is very low, so that the processes are industrially not useful.
As the other process, a process of azeotropic dehydration of an aryl methyl ketone and a glyoxylic alkyl ester alkyl acetal under heating in the presence of an acid (JP-A-4-235142) has been reported. However, the glyoxylic alkyl ester alkyl acetal is very expensive and stable supply thereof on an industrial scale is also problematic.
In addition, Friedel-Crafts acylation of an aromatic hydrocarbon with a dicarboxylic acid monoester halide in the presence of an acidic catalyst (JP-A-2-10816) has also been reported. However, the process has defects that the dicarboxylic acid monoester halide is difficult to obtain, control is difficult owing to a low yield at the synthesis and a formation of a large amount of by-products, stable supply on an industrial scale is also problematic, and the like.